Silicone compositions have long been used as release coatings, which are useful in many applications whenever it is necessary to provide a surface or material which is relatively nonadherent to other materials which would normally adhere thereto. For example, silicone release compositions are widely used as coatings which release pressure-sensitive adhesives for labels, decorative laminates, transfer tapes, etc. Silicone release coatings on paper, polyethylene, Mylar.RTM., and other such substrates are also useful to provide non-stick surfaces for food handling and industrial packaging applications.
Previously developed silicone paper release compositions, such as those described in copending U.S. application Ser. No. 267,091, filed May 22, 1981, now U.S. Pat. No. 4,340,647, and U.S. application Ser. No. 359,480, filed Mar. 18, 1982, now abandoned, have been heat curable, but silicone resins which could be cured with exposure to ultraviolet light are desirable.
Ultraviolet light is one of the most widely used types of radiation because of its relatively low cost, ease of maintenance, and low potential hazard to industrial users. Typical curing times are much shorter, and heat-sensative materials can be safely coated and cured under UV light where thermal energy might damage the substrate.
UV-curable epoxy-functional silicones have been disclosed in U.S. Pat. No. 4,069,368 (Deyak) and U.S. application Ser. No. 063,168, filed Aug. 3, 1979, now abandoned. Because of their high reactivity, vinyloxy-functional silicones are highly attractive, but until now only the preparation of vinyl ether trialkoxysilanes, in Ger. Offen. No. 2,159,723 (9/14/73; Bier et al.), has been described; the successful synthesis of vinyloxy-functional silicone polymer resins has not been reported.
It has now been discovered that photo-curable vinyloxy-functional polysiloxane resins can be efficiently produced which are catalyzed by a wider variety of curing catalysts than the aforementioned epoxy-functional silicones and, when applied as release coatings to a substrate, cure to a tack-free, no-smear, abhesive surface in as little as 0.15 seconds. The extremely rapid potential cure rate of these materials, and their compatibility with onium salts heretofore believed ineffective for ultraviolet-triggered polymerizations, makes the vinyloxy-functional polyxiloxanes of the present invention extremely attractive to the silicone release coating and other industries.